1. Field of the Invention
The present invention relates to a fluorine-containing copolymer elastomer, a process for producing the same and a composition containing the same, and more particularly to a novel fluorine-containing copolymer elastomer having bromine groups as cross-linkable groups, which can give vulcanization products having distinguished resistances to chemicals, low temperature and heat, a process for producing the same and a composition containing the same.
2. Description of Related Art
Fluorine-containing elastomers prepared by copolymerization of tetrafluoroethylene with perfluoro(methyl vinyl ether) have distinguished resistances to chemicals and heat, and thus are used as various machine parts such as O-rings, diaphragms, etc. at positions requiring higher resistances to chemicals and heat. However, these fluorine-containing elastomers have a poor resistance to low temperature and accordingly are not applicable to positions requiring a resistance to low temperature.
To improve the resistance to low temperature, while maintaining high resistances to chemicals and heat, it was proposed to replace the CF.sub.3 group of perfluoro(methyl vinyl ether) CF.sub.2 .dbd.CFOCF.sub.3 with a perfluoroalkyl group having an ether bond.
One known example thereof is copolymerization of tetrafluoroethylene with a compound having the following general formula: EQU CF.sub.2 .dbd.CFOCF.sub.2 CF (CF.sub.3)O!nC.sub.3 F.sub.7
as disclosed in JP-B-61-57324, JP-B-62-34246, JP-B-63-25003, JP-A-60-23407, etc., where no improvement of the resistance to low temperature as desired for the copolymer was obtained without the n value larger from the viewpoint of molecular structure, whereas a larger n value made the molecular weight larger and consequently considerably lowered the polymerizability. This was a serious disadvantage.
To improve the resistance to low temperature, it was also proposed to add a plasticizer such as a perfluoropolyether compound represented by the following general formula: EQU RfOCF (CF.sub.3)CF.sub.2 O!nRf'
where Rf and Rf' each are a perfluoroalkyl group, to the fluorine rubber. Addition of such a plasticizer improve the resistance to low temperature of fluorine rubber vulcanization products, but the plasticizer tend to bleed out of the vulcanization product surfaces and dissipate when used under high temperature conditions for a long time, and thus the resistance to low temperature is gradually lost. Even at a relatively low service temperature, dissipation of the plasticizer is not negligible under high vacuum conditions.
Furthermore, the resistance to low temperature can be improved by blending with other elastomer having a good resistance to low temperature, for example, fluorosilicone rubber, but the preferable proper characteristics such as resistance to chemicals will be deteriorated.